1. Field of the Invention
The present invention is directed to optical transceivers and methods for their operation.
2. Description of the Prior Art
Fiber-optic gyros are employed, for example, in navigation systems. Fiber-optic gyros for use in inertial navigation systems (INS), requiring high accuracy, are typically based on highly stable superfluorescent light sources with wavelengths of about 1550 nm. The wavelength dependency of superfluorescent light sources upon temperature at 1550 nm is typically 10 ppm/° C. Its improvement to about 0.05 ppm/° C. can only be achieved by using wavelength-stabilizing elements such as thermally compensated Bragg gratings.
Superluminescent light-emitting diodes (SLDs) are inexpensive semiconductor light sources that are significantly less stable. This has previously prevented their use in fiber-optic gyros for systems having high accuracy requirements. SLDs have comparatively low scale factor accuracy which results primarily from their wavelength instability. For instance, the wavelength of an SLD is strongly temperature-dependent with temperature drift of about |dδ/dT|=400 ppm/° C. Another cause of wavelength instability is the aging typical of semiconductor sources. As a result, the wavelength of the SLD increases and the power delivered decreases with increasing operating time.
German patent application DE 103 07524 A1 describes a method for sending the spectrum of an SLD onto an external wavelength reference for stabilization in the form of one or two fiber Bragg gratings. The required technology is complex and expensive. Furthermore, additional light losses are to be expected.
U.S. Pat. No. 7,228,022 B1 describes an integrated optical transceiver comprising a superluminescent light source and a temperature regulating unit. Light radiated by the light source is coupled via the light waveguide into a fiber-optic gyro. Light extracted from the fiber-optic gyro is sent into the detector.